What is a Trio Sonata?

The first thing to realise is that, unlike many other ancient genres, the trio sonata doesn’t exist any more; nobody composes them, not even ‘ironically’. Which is surprising when you consider that for most of the Baroque period it was the dominant form in European chamber music, and one whose basic texture reached into vocal and orchestral composition too.

Ah yes, the texture. The second thing to note, you see, is that a trio sonata is more often played by four instruments than three, but can also be played by two or even one. This is because the word ‘trio’ refers not to the number of instruments in the music, but to the number of contrapuntal threads. (Doesn’t musical terminology drive you mad sometimes?) The most common disposition is two upper lines of equal status (two violins, say, or two recorders), and a bass line (typically played by a cello or a viola da gamba). This bottom line, however, is a basso continuo, meaning that one or more chordal instruments, such as a harpsichord or theorbo, can be added to it to provide semi-improvised ‘fill-in’ harmonies. Yet Bach’s sonatas for violin and harpsichord (in which the harpsichord plays the bottom line and one of the upper ones) or his organ sonatas (in which keyboards and pedals play all three between them) are also essentially ‘trio sonatas’. Many orchestral pieces, too, such as Corelli’s concerti grossi, could be seen as being in a ‘padded-out’ trio sonata texture.

While the texture can be regularly spotted in the early 1600s in Italian music both instrumental and vocal (think of Monteverdi’s Zefiro torna), the rise of the violin as a ‘serious’ instrument in the 17th century undoubtedly shaped the direction things would go. Thus we get more and more standardised string trio sonatas as the century moves on, until a peak comes in the four sets of Sonate a tre by Corelli, published between 1681 and 1694. They became the classic models for the next seven decades, inspiring composers such as Couperin, Purcell, Vivaldi, Bach, Handel, Telemann – all of whom conformed to it while finding plenty of room for their own personalities – as well as countless lesser names.

No doubt the ingeniously intertwining lines of the trio sonata and the fact that it prized fluent conversational interchange over unsettling drama and inconvenient virtuosity contributed to its popularity with professional and amateur musicians alike; trio sonatas continued to be published in numbers well into the mid-18th century. In the end, however, the emerging Classical style ousted it with its (entirely separate) development of the string quartet and the instrumental sonata with keyboard accompaniment, and so far music history has not swung back in its direction.